Mobile terminals such as a mobile phone, a Personal Digital Assistant (PDA) and the like are driven with rechargeable batteries due to their nature, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, since the contact terminal is outwardly protruded in such a contact type charging scheme, the contact terminal is easily contaminated by foreign substances and thus the battery charging is not correctly performed. Further, the battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Recently, a wireless charging or a non-contact charging technology is developed and used for electronic devices to solve the above-mentioned problem.
Such a wireless charging technology employs wireless power transmission/reception, and corresponds to, for example, a system in which a battery can be automatically charged when a portable phone is not connected to a separate charging connector but merely placed on a charging pad. Generally, the wireless charging technology is applied to a wireless electronic toothbrush or a wireless electronic shaver and has been made known to the public. Accordingly, a waterproof function can be improved since electronic products are wirelessly charged through the wireless charging technology, and the portability of electronic devices can be increased since there is no need to provide a wired charging apparatus. Therefore, technologies related to the wireless charging technology are expected to be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and an RF/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected that the day will come when all electronic products are wirelessly charged, anytime and anywhere, without a wire in the near future on the strength of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting power between a first coil and a second coil. When a magnet is moved in a coil, induction current is generated. By using the induction current, a magnetic field is generated at a transmission side, and electric current is induced according to a change of the magnetic field so as to make energy at a reception side. The phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has high energy transmission efficiency.
With respect to the resonance scheme, Prof. Soljacic of MIT announced “Coupled Mode Theory” in 2005, in which electricity is wirelessly transferred using a power transmission principle of the resonance scheme even if a device to be charged is separated from a charging device by several meters. The wireless charging system of MIT uses a physical concept of resonance in which a wine glass near to a tuning fork resonates with an identical vibration frequency when the tuning fork resonates. The research team made an electromagnetic wave containing electrical energy resonate instead of making sound resonate. The resonated electrical energy is directly transferred only when there is a device having a resonance frequency and parts of electrical energy which are not used are reabsorbed into an electromagnetic field instead of being spread in the air, so that it is considered that the electrical energy does not affect surrounding machines or people unlike other electromagnetic waves.
According to the wireless charging with the resonance scheme, when a wireless Power Transmission Unit (PTU) has been communicated with a wireless Power Reception Unit (PRU), the PRU and PTU exchange own static parameters and then transmit information on own state to a counterpart.
In this event, a value included in the static parameter is configured with reference to a Continuous Current (CC) mode of a battery which is the most common state and is previously stored in a memory of the PRU. When power has been transmitted from the PTU so that a communication with the PRU has been performed, the power is transmitted to the PTU.